Referring now to FIG. 1, a top view is presented of an example of a known configuration for an automated storage system for preparing packages comprising:                a warehouse 7 comprising several sets (two in this example) each formed by an alley 7a, 7a′ feeding, on either side, a storage shelf 7b, 7c, 7b′, 7c′ with several superimposed stacking levels;        a set of conveyors taking source loads from the warehouse up to the preparation or preparing stations and vice versa. In the example of FIG. 1, three sub-assemblies of conveyors referenced 6, 8 and 9 respectively can be distinguished;        several customer order preparation stations 10a to 10f, each occupied by an operator 1a to 1f and extending perpendicularly to the conveyors of the third sub-assembly referenced 8; and        a management system (also called a “management unit”) that is a computer-based central management system responsible for driving the entire automated storage system (warehouse, set of conveyors and preparing stations).        
The management system also manages the list of customer orders associated with each shipping container (target load) and therefore the sequential order of the customer order lines forming this list, as a function of the location of the storage containers (source loads) in the warehouse, the availability of the trolleys and the elevators of the warehouse as well as the requirements in terms of items and goods of the different shipping containers to be prepared which succeed one and other at the preparing station. The purpose of this is to optimize all the movements and the preparation time for the shipping containers and ensure synchronization between the arrival, at the preparation station, of a shipping container and storage containers (containing goods indicated in the customer order list associated with this storage container).
In the example of FIG. 1, each preparing station comprises two conveyor circuits: a first conveyor circuit for the storage containers, formed by two horizontal columns of conveyors; one column (the outbound column 2) for moving these storage containers from the third sub-assembly of conveyors 8 up to the operator 1a and the other (the return column 3) for the reverse movement and a second circuit of conveyors for the shipping containers, formed by two horizontal columns of conveyors: one (outbound column 4) for moving the shipping containers from the third sub-assembly of conveyors 8 up to the operator 1a and the other (return column 5) for the reverse movement. In each of these first and second circuits, the outbound columns 2 and 4 (formed by classic horizontal conveyors) carry out the function of accumulating a determined quantity of containers upstream to the operator (or automaton).
A storage container makes the following journey: it is picked up by a trolley in the warehouse 7 then conveyed successively by the conveyors of the sub-assemblies 9, 6 and 8 and then by the conveyors of the outbound column 2 and then presented to the operator. In the other direction (after presentation to the operator), the storage container makes the reverse journey: it is conveyed by the conveyors of the return column 3 and then successively by the conveyors of the sub-assemblies 9, 6 and 8 and finally re-positioned in the warehouse 7 by a trolley.
As mentioned further above, the storage containers (source loads) have to be presented to the operator in a desired sequential order forming a determined sequence. This is the same for the shipping containers (target loads). In addition, the stream of storage containers must be synchronized with the stream of shipping containers.
In order to relax the constraints on the warehouse, it is accepted that the containers (storage containers or shipping containers) will not exit the warehouse in the desired sequential order (i.e. in the order in which they have to be presented to the operator). An operation therefore needs to be carried out for sequencing the containers between the warehouse and the preparing station where the operator is situated.
In the example of FIG. 1, this sequencing operation is performed by the second sub-assembly of conveyors 6 which itself fulfils the buffer role: the storage containers circulate therein in a loop and when the storage container awaited on the conveyors of the outbound column 2 comes before this column (in order to complete the sequence of storage containers awaited at the preparing station), this container is transferred to the conveyors of the outbound column 2, the other storage containers continuing to circulate on the second sub-assembly of conveyors 6. This method is performed for each of the storage containers awaited in the sequence (i.e. in the sequential order of arrival desired at the preparing station).
Classically, this sequential order (sequence) of arrival is pre-determined (i.e. it is determined for each container before this container reaches the preparation station) by the management system and, if necessary, recomputed during the carrying of the containers from the warehouse exit to the preparing station in which the operator is situated (for example take into account a malfunction in an element of the system).
In the example illustrated in FIG. 1, the return column for the shipping containers 5 is common to the preparation stations referenced 10a and 10b (these two adjacent stations are configured symmetrically to each other, the common column forming an axis of symmetry). This is also the case for the adjacent preparing stations referenced 10c and 10d as well as for those referenced 10e and 10f. This approach is aimed at reducing the footprint of the preparing stations.
Unfortunately, despite this clever approach, the current solution based on horizontal classic conveyors (as described here above with reference to FIG. 1) has several drawbacks.
First of all, it consumes to very large amount of m2 for a small running surface height (750 mm typically). An example of this excessive footprint is the fact that the surface area needed for six order-preparing stations (as in the example of FIG. 1) is about 100 m2.
Another drawback is that the density on the ground of classic horizontal conveyors in preparing stations is such that it makes it difficult to obtain maintenance access to these conveyors (the conveyor coverage area is too dense).
Another drawback is that, without further increasing the footprint of the preparing station (by increasing the length of the outbound column of each of the first and second circuits), it is not possible to increase the number of containers that can accumulate upstream to the operator (or automaton).
Yet another drawback is that, in certain configurations, the footprint of the preparing stations prevents maintenance access or makes it difficult to obtain maintenance access to the trolleys (also called shuttles) used in the warehouses. The maintenance of these trolleys sometimes then makes it necessary to access the warehouse by the rear, with a girder system (referenced 11 in FIG. 1) that is hardly ergonomic.
Yet another drawback is that it is not possible to achieve optimal processing when one and the same container has to be presented to the operator several times in succession. Indeed, at present, the sub-assembly of a conveyor referenced 6 is used to carry out an operation for re-introducing the given storage container into the outbound column 2 of the first preparing station circuit (10a for example). This is not optimal because the time slot between two successive instances of presentation of the same container to the operator cannot be short, and corresponds to the duration of travel by this container on the totality of the following circuit: conveyors of the return column 3 and then those of the sub-assembly of conveyor referenced 6, and finally those of the outbound column 2. In practice, if this time slot is too great, then two storage containers containing the (same) type of desired items are made to exit the warehouse. Then, the number of movements made by the warehouse is increased. This is not a satisfactory solution (because it generally leads to an increase in the number of alleys of the warehouse in order to avoid surpassing a maximum capacity of entries/exits that can be made by the elevator or elevators positioned at each end of an alley).
In order to overcome the above-mentioned drawbacks of the classic technique, a solution has been proposed in the patent EP2487123A1 (Savoye). It consists of the use of at least one chute in combination with at least one alternating elevator. The chute comprises superimposed mobile locations each capable of receiving and moving at least one load (container) downward. The chute forms a means of vertical accumulation and sequential distribution of loads preliminarily placed in the locations. The alternating elevator is capable of moving vertically along the chute up to each of its locations. For each given load that comes up, the managing system reads its identifier then selects one of the locations of the chute (depending on the identifier read and on a pre-determined sequence, defining the sequential order in which the loads must exit the chute in order to be presented to the preparing station) and finally steers the elevator in order to make the given load enter the selected location.
In being based on a vertical accumulation of loads, the prior-art solution described in EP2487123A1 has several advantages. In particular it:                reduces the footprint of the order preparing stations;        facilitates maintenance access to the elements included in the preparing station (the conveyor coverage area is not too dense);        increases the number of loads that can be accumulated, without negative impact on the footprint of the preparing station; and        facilitates maintenance access for the trolleys used in the warehouse.        
In addition, the combined use of a path and alternating elevator enables the performance of a sequencing (i.e. a scheduling in the sense of placing the loads in a desired sequential order called a sequence). It may be recalled that the loads do not exit the warehouse in the desired order and have to be sequenced (scheduled) before being presented to the operator (or robot). The sequencing (scheduling) capacity is related to the quantity of loads that can be stored temporarily in the path.
The prior art solution of EP2487123A1 however has several drawbacks, especially:                it is limited in performance by the fact that it requires the use of one or more alternating elevators;        it is not a multi-format solution with respect to the chutes; and        it requires two distinct pieces of equipment (elevator and chute) used in combination to create sequences, and this increases its cost.        